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Windprofiler Radars and detection of STE events

Explore the capabilities of windprofiler radars in detecting and analyzing Severe Thunderstorm Events (STE). Discover how these radars generate high-intensity radiation beams and steer them to capture meteorological data such as winds, turbulence, and backscattered power. Learn about the Canadian approach of spreading multiple radars across the province to gain a significant meteorological advantage at a lower cost.

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Windprofiler Radars and detection of STE events

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  1. Windprofiler Radars and detection of STE events W.K. Hocking University of Western Ontario

  2. Radar. Small airport radars to giant dishes…

  3. Purpose – to create a narrow beam of radiation, of VERY high intensity.

  4. Japan MU radar Looks like a dish…

  5. Zoom in… > $10M for 1 radar in 1985!!

  6. With a dish, we can move it around … But even if we cannot do that with our radar, we CAN steer the beam by feeding different signals to different antennas – the whole beam can be steered in a fraction of a second!

  7. The Canadian approach… Effective, and much cheaper…

  8. Require: High Power – 40 kW in short bursts c.f. Japan and Germany – 1 MW. But our system is still effective, and by spreading multiple radars across the province, we gain great meteorological advantage.

  9. Receiving and Digitization System

  10. Beam Steering Unit

  11. Highly sensitive receivers are needed – transmitted signal is kilovolts, but received signal is microvolts! Special signal processing is required – coded pulses, coherent integration, spectral fitting…

  12. Measure winds, turbulence, backscattered power.

  13. Armin Dehghan, poster

  14. Relation to Ozone?

  15. Radar/Ozone

  16. Why is there enhanced scatter at the tropopause? • Specular Reflectors

  17. Sheets…. Common in regions of HIGH STATIC STABILITY e.g. tropopause.

  18. Turbulence

  19. When people talk about turbulence, they often talk about “eddies”. We often envisage turbulent particle trajectories to be elliptical in shape...

  20. “Eddies” (Laboratory photographs of tracers)

  21. Due to the velocity shears (differential velocities) in the fluid, even initially isotropic objects are stretched and torn apart ...

  22. Computer simulations showing vorticity strings in a patch of turbulence (Werne, Fritts et al.)

  23. There are also various stages of turbulence - developing, steady-state, and decaying.

  24. Enhanced VHF signal due to EITHER specular reflections or turbulence

  25. Cause of upper level turbulence – Gravity Waves. It may appear in patches of limited extent...

  26. Gravity waves propagating upward increase In amplitude as they encounter regions of high static stability. Can result in turbulent layers just above the tropopause.

  27. ---------  Layering z z x x

  28. Energy deposition - at the smallest scales, large wind-shears produce fluid frictional heating (deposition of kinetic energy). We talk about the “energy dissipation rate” Energy may also be dissipated by deposition of potential energy. Turbulence may in fact also function as a storage mechanism of energy.

  29. C. Diffusion... Diffusion is often represented by an “eddy diffusion coefficient”, using an analogy with molecular diffusion. But this grossly over-simplifies the process of turbulent diffusion in the atmosphere. Different diffusion mechanisms apply at different scales.

  30. 4. What are the unique aspects of turbulence pertaining to the atmosphere? In the atmosphere, turbulence is:  Spatially and temporally variable and intermittent  Frequently anisotropic  Driven by multiple phenomena, some of which themselves are scale dependent.  Subject to unique measures of stability (Richardson number compared to Reynolds number, Froude number etc.)  Species-dependent (ions compared to electrons compared to neutrals)

  31. Layered structures higher up ...

  32. LAYERING in Turbulence Fully developed turbulence (FM-CW radar, Eaton et al.)

  33. Czechowsky et al.

  34. Relevance here? Homogeneous Turbulence: n = c s l, s = molecular diameter, l = mean free path. K = Lv, L = “eddy size”, v = associated velocity. K = L2/T, L = dimension, T = time scale. L = (KT)1/2

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